(1) Field of the Invention
The present invention relates to a method of manufacturing an electronic component built-in wiring board incorporating therein an electronic component which is accommodated in a cavity provided in an insulating layer.
(2) Description of the Related Art
In recent years, an electronic component has been highly densified and functionalized in response to a demand for high performance and miniaturization of an electronic device. As a result, a wiring board capable of high-density packaging of an electronic component is demanded. As such a wiring board, an electronic component built-in wiring board has been developed (Japanese Patent Application Laid-Open No. 2007-005768).
First, with reference to FIG. 4, a description will be given of one example of an electronic component built-in wiring board B which is manufactured according to a conventional method of manufacturing. The wiring board B includes an insulating board 21, a wiring conductor 24, a solder resist layer 26 formed on the insulating board 21 and the wiring conductor 24, and an electronic component D accommodated in the insulating board 21.
The insulating board 21 includes a first insulating layer 21a, and second insulating layers 21b, 21b laminated on upper and lower surfaces of the first insulating layer 21a. A cavity 22 for accommodating therein the electronic component D is formed in the first insulating layer 21a. In the cavity 22, the electronic component D is accommodated while the electronic component D is fixed by parts of the second insulating layers 21b, 21b. 
Further, a through-hole 23 is formed in the first insulating layer 21a. The wiring conductor 24 adheres to the upper and lower surfaces of the first insulating layer 21a and inside the through-hole 23. With this arrangement, the wiring conductors 24, 24 on the upper and lower surfaces of the first insulating layer 21a are electrically connected to each other via the through hole 23.
A plurality of via holes 25 are formed in the second insulating layer 21b. The wiring conductor 24 also adheres to a surface of the second insulating layer 21b and inside the via holes 25. A part of the wiring conductor 24 on the surface of the second insulating layer 21b is electrically connected to the wiring conductors 24, 24 on the upper and lower surfaces of the first insulating layer 21a via the via holes 25. Further, a different part of the wiring conductor 24 on the surface of the second insulating layer 21b is electrically connected to an electrode T of the electronic component D through the via holes 25.
The electronic component D includes, for example, a chip capacitor for stabilizing power supply to a semiconductor element S, and the like.
Further, a part of the wiring conductor 24 formed on the upper surface of the second insulating layer 21b on an upper surface side is exposed in an opening 26a formed in the solder resist layer 26, and forms a semiconductor element connecting pad 27. Then, by connecting an electrode of the semiconductor element S to the semiconductor element connecting pad 27 via a solder bump, the semiconductor element S is mounted on an upper surface of the wiring board B.
Further, part of the wiring conductor 24 formed on the lower surface of the second insulating layer 21b on a lower surface side is exposed in an opening 26b formed in the solder resist layer 26, and forms an external connection pad 28 for connection to an external electric circuit board. Then, by connecting the external connection pad 28 and an electrode of the external electric circuit board to each other, the semiconductor element S is electrically connected to the external electric circuit board, and the semiconductor element S operates by transmitting a signal between the semiconductor element S and the external electric circuit board via the wiring conductor 24 and the electronic component D.
Next, with reference to FIG. 5A to FIG. 6I, a method of manufacturing the conventional wiring board B will be described. Here, FIG. 5A to FIG. 6I illustrate schematic cross sectional views of principal portions of individual manufacturing steps.
First, as illustrated in FIG. 5A, the wiring conductor 24 adheres to the upper and lower surfaces of the first insulating layer 21a in which the through hole 23 penetrating from the upper surface to the lower surface is formed, and inside the through hole 23. The wiring conductor 24 is formed by, for example, a well-known semiadditive method or subtractive method.
Next, as illustrated in FIG. 5B, the cavity 22 is formed in the first insulating layer 21a. The cavity 22 is formed by, for example, blasting or laser processing.
Next, as illustrated in FIG. 5C, the first insulating layer 21a is placed on an adhesive sheet N.
Next, as illustrated in FIG. 5D, the electronic component D is inserted into the cavity 22, and the electronic component D is placed on the adhesive sheet N which is exposed in the cavity 22.
Next, as illustrated in FIG. 5E, the second insulating layer 21b is laminated on an upper side of the first insulating layer 21a. Generally, the second insulating layer 21b is laminated on the upper side of the first insulating layer 21a under a vacuum condition. With this arrangement, the second insulating layer 21b can be brought into intimate contact with the first insulating layer 21a firmly.
Next, as illustrated in FIG. 5F, the adhesive sheet N is peeled off.
Next, as illustrated in FIG. 6G, the first insulating layer 21a is laminated on the upper surface of the second insulating layer 21b. With this arrangement, the insulating board 21 is formed.
Then, as illustrated in FIG. 6H, the via hole 25, which exposes the electronic component D and the wiring conductor 24 on the first insulating layer 21a from the surfaces of the second insulating layers 21b, 21b, is formed. Thereafter, the wiring conductor 24 adheres to the surface of the second insulating layer 21b and inside the via hole 25.
Finally, as illustrated in FIG. 6I, the wiring board B is formed by adhering of the solder resist layer 26 including a first opening 26a and a second opening 26b which expose therein the wiring conductor 24 formed on the second insulating layers 21b, 21b. 
However, when the wiring board B is formed according to such a method, the adhesive sheet N and the first insulating layer 21a are brought into intimate contact with each other firmly by an influence of a step for firmly bringing the second insulating layer 21b into intimate contact with the upper side of the first insulating layer 21a under the vacuum condition as described above. As a result, in the step of peeling off the adhesive sheet N from the first insulating layer 21a, an adhesive of the adhesive sheet N may remain on the surface of the first insulating layer 21a. In this way, if the adhesive remains on the surface of the first insulating layer 21a, adhesion between the first insulating layer 21a and the second insulating layer 21b is disturbed, separation between the two may be caused, and insulation properties between the wiring conductors 24 may become insufficient. As a result, this causes a problem of reduced insulation reliability of the wiring board B.